JUST CAUSE UNLOCKABLES
Grapple hook
After level 2 there are territories you can take over. Once you have done about three of them you will get the grapple hook.
Helicopter
When you get your grapple hook fire it at a passing or attacking helicopter. Then, just reel your self in.
Agency jeep
After you kill the man on the boat and finish the mission, you will get the agency jeep.
20 Land Vehicle Stunts
Steal two cars. Face one forward, then park the other one sideways in front of the car. Get into the stunt position, then the "B Jump to Roof" option should be on top. Just press B(20) to get the achievement.